(Letter dated March 18)
In this article Matthew expands on his views of the evolution of human races (see also Note C of his appendix to On Naval Timber and Arboriculture). For Matthew, the differences between human races were both genetic and cultural, and indeed because of his belief in Lamarckian inheritance the distinction between the two is blurred. These qualities could persist in different sub-classes in the same country. Thus the aristocracies of both Britain and France were Teutonic in origin (superior stock, explaining how they came to rule). But natural selection was now working against them due to their dissolute lifestyles, which explained the French Revolution:
“This class, become enervate and worthless under the comparative warm climate and luxurious dissipated habits of France, were driven out by the Celtic climate-suited aborigines, who constituted the great body of the working population”

For Matthew, the subsequent history of France, including the rules of Napoleon I and III, was all foreseeable:
“All this is a natural sequence, and might have been foretold to a nicety”

Matthew then provides some examples of how war can act as an agent of selection in human populations, though leading to deterioration of breed rather than improvement, through the removal of the most worthy men in combat:
“It has been stated that these wars have lowered the average height of the French people about 2 inches; the natural result of the elite of the men of France being all carried off in their early youth by Napoleon, to be butchered, or killed by over-marching and campaigning hardships, and only the infirm, the lame, the dwarfish, the refused of the army surgeon, left at home, of whom the present generation are the progeny”

Matthew thought the same process had occurred in Spain, explaining their well-known slothful nature:
“The contest between the Goths and Moors in Spain was not less injurious to the race of the Spaniards. The result of competition in war betwixt men is very different from that of natural selection of organism in the wilderness. In war, when the soldiers are not raised by bounties, it is the bravest and strongest who are destroyed.”
“Those long-continued wars account for the Spanish want of energy in modern times, and it only required the drain of the most enterprising of the remainder in the brigandage expeditions to Central and South America, to give to Spanish energy the finishing blow.”

Matthew then argues that a country with a strong organised religion (e.g. Catholism) cannot fulfil its potential (an idea that Matthew also returns to in his fifth letter in Schleswig-Holstein):
“A good working people-represented government can only exist where no priesthood have controlling power. I cannot believe that a representative Government can work advantageously with a population under priest influence, such as the Romish Church, the confessional and religion-monopoly afford. Let Italy and France look to this! Excepting in the case of France under the first republic, it is only Teutons who as yet have protested against Priest domination.”

In a footnote, Matthew again refers to his prescience in describing the benefits of iron-clad steam-powered war ships in On Naval Timber, and, reflecting his previous involvement in the Chartist movement, the benefits of extended suffrage.

Finally, Matthew returns to an application of selection (“although in a different direction to my theory of natural selection”) in relation to increasing skull thickness (and thence stupidity) in Australian aborigines due to their practice of striking each other’s heads in combat (an example he also gave in Emigration Fields). As in the book, he then extends this mechanism to the British aristocracy (but via fox-hunting rather than the medieval jousting used in the book), and also to the Irish (but pointedly not the Scots):
“A curious system of war existed among the native population of New Holland [Australia] previous to its occupation by the British, which accounts for the low grade even of savage life in those regions. It was the gentlemanly or chivalric code of fighting, for each party alternately to present the top of their head to receive a knock from their opponent’s club, till one of the antagonist parties had enough. Whenever there was a head without a great block of thick bone covering and protecting, but crushing the brain and preventing its expansion, the owner was killed off hand, or his brain so stunned or addled as to render him disqualified to be a Thales, Numa, or Moses. This practice, in pretty constant operation for a lengthened period of time would act in a similar manner to modify the race, though in a different direction to my theory of natural selection, and must have served to stultify — lower the mental capacity of the race. The same may have operated in a less degree in a country nearer home — “With the Sprig of Shillelagh” [Irish oak club previously used in combat]. It is stated that the scull of the celebrated Scot, George Buchanan, was examined after his death, and found to be as thin as a wafer. In Germany, whence the British race derive their mental as well as physical stamina, mothers tie an elastic roll of about 1½ inch diameter of feather, wool, &c., round the head of their children at the brow, to prevent them in their numerous falls in infancy from addling their superior brains. Those of our fox-hunters who tumble as often as the children, and who may have brains worth protecting, should follow the same practice.”